Method of preparing a fluorescent screen



METHOD OF PREPARING A FLUORESCENT SCREEN Albert Kenneth Levine, Jersey City, N. ,J., assignor to Sylvania Electric Products Inc., a corporation of Massachusetts No Drawing. Original application September 27, 1951,

' Serial No. 248,661. Divided and this application November 17, 1953, Serial No. 392,753

8 Claims. or. 96-35 This invention relates to a. method of preparing a cathode ray screen. More particularly, it relates to a method suitable for preparing cathode ray screens coated with a plurality of phosphors positioned thereon in a desired pattern.

This application is a division of application Serial Number 248,661 filed September 27, 1951 entitled Screen for Color Television]? The cathode ray screen of the all-electronic. color .pic-' ture tubes-which are at present under consideration consist of a group'of symmetrically placed dots or lines of phosphors on a glass screen. ticular consists of an array of some351,000 dots of phosphor? on a9" x 12" screen arranged in clusters of three dots;including one each of the primary colors. Each cluster of three dots must be suitably located with re spect to a corresponding hole in. a thin perforated metal sheet placed a short distance (about 0.8) from the phosphor screen if the cathode ray tube is to give "the desiredto variations in dot sizes which arexbrought about by the incr'easedspacing between the printing mask and plate caused bythe presence of the first series of dotson the glass screen. When printing techniquesare used it" is most difficult to obtain the needed degree of accuracy One screemdesign in par-' F ICE is thoroughly mixed with a quantity of fine phosphor powder to which a sensitizing material may be added if another layer of photosensitive material into which 'has of registration. a In fact, all of the methods which haive heretofore been tried for making these tri-color' screens have only been suited for hand operation where a small number of screens were needed but not for any method which might-bet considered commercially economical.

It is anobject of this invention to provide a commercially economical method of making a screen in which theiphosphor'is laid down in a particular, predetermined design. 7

It is a further object of this invention to provide a method for making screens having a plurality-of phosphors by a method which is adapted for commercial production. 33

It is a still further object of this invention to provide a simple method of making a tri color screen in which the various phosphors Will be accurately spaced witli're spect to one another. g 7

In accordance with this invention, these objects and screen.

-" In"a"ccordance with the preferred method ofinv ena tion, for example, a photo-sensitive film forming' material However, aphotographic plate having the in place of the aperture plate.

After the exposure to light has been completed the exposed plate is Washed with a'solvent for the'photosensi tive film. This will leave an array of dots consisting of phosphor incorporated in the light-fixed photosensitive material remaining on the glass'panel. This .is then allowed to dry whereupon the glass panel is coated with been incorporated a second phosphor which will-emita different color under cathode ray bombardment. After drying the second layer the aperture plate or the photo-- graphic plate is registered with respect to the existing sets of dots whereupon the plate is again exposed to light, washed and dried. This procedure will have deposited the second set ofdots on the plate. To obtainthe' third set. of dots it is only necessary to repeat the procedure usinga photosensitive film forming material into which] has been incorporated a third phosphor material, re

registering the aperture plate or photographic platefexposing the coating to light, Washing and drying the plate. I This will leave a three dot array on the glass panel which can then be baked to gasify and'drive off the volatile in gredients and leave the phosphor on the plate'in the deaphosphor pattern of any design.

In another modification of this invention in which photosensitive film is used for the making of the tri-color screen, a photosensitive film forming material of a light hardenable photo resist is used to place a coating on the dry glass on which the screen is to be formed and withthis particularmodification no phosphor is included in the film. Afterthis film has been dried it is subjected to light through a'plate which transmits light to all portions of the film other than those at which it'is finally V desired to have the phosphor present on the glass. The

exposed plate is then washed to remove the film of photo resist from those areas which have not been subjected to light. In the case of a dot pattern this'leaves a light" hardened film on the glass having aseries of holes at those place where the dots of phosphor are to remain. After thelight hardened film of photo resist has been dried the holes are filled with an adhesive, forexample,

ethyl silicate, and a powdered phosphor of a desired color Alternatively, the phosphor may be incorporated 'into the adhesive and the holes filled with this mixture. Thereupon, the remaining film is removed by "a suitable method such as immersing in hot 3% hydrogen peroxide or in an enzyme solution is either brushed or settled thereon.

leaving behind the phosphor dot pattern on the glass;

The panel is again dried'and coated with a sensitized photosensitive film. This film i'sagain covered with a photographic plate containing a pattern of black dots which have been properly oriented with respect-to the first series of dots whereupon the film is exposed to a suitable light source, washed to remove the unexposed film leaving a second series of holes which are again-filled "f p with adhesive and brushed with a second phosphor(or "with adhesive into which 'is incorporated phosphor) whereupon the remaining film is again removed solvent leaving the two sets of'phosphors behind; The; process is againirepeated to place the third set ofidots"; I .on the glass panel. I

There are quite a number of photosensitive film materials which are available and adaptable for use in accordance with this invention. The most common are, for example, polyvinyl alcohol, polyvinyl acetate, gelatin, glue, shellac and photosensitive materials of the type produced byv the photographic material manufacturers. Some of thesematerials required the addition of a sensitizing material which is usually an oxidizing material, the. most common of which is a bichromate salt such as is used in the silk screening art.

1 In accordance with a preferred example a photosensitive film for a tri-colored screen can be prepared as follows: 70.8 grams of polyvinyl alcohol whose 4% solution at.20 C. has a viscosity, of 20 to 2 5 centipoises is dispersed in 470 cc. of cold water by means of vigorous agitation. The dispersion is then stirred and warmed to a temperature of 80 C., this temperature being maintained until the dispersion isclear whereupon it is filtered to remove any undispersed particles. To this dispersion is then added 20 grams of finely dividedphosphor from which large particles and agglomerates have been removed. This mixture is milled until the phosphor is uniformly dispersed whereupon 30cc. of 0.4 molar ammonium bichromate is added and the mixture is milled for two minutes. Since this material is light-sensitive,

doctor-blade across the film. A. good example of thick-' ness of filmis; about 0.008". The film is then dried in the. dark and is ready for exposure. After exposure. through a photographic plate the unexposed portions can be washed off with water. This leaves an array of dots. The plate is then driedand given another coating with the photosensitive phosphor containing film and exposed and washed togive a second set of dots. The procedure of coating, exposing and washing is repeated until the desired tri-dot pattern is obtained, after which the glass panel is baked in: a furnace at a temperature ranging between 400 and 500 C. This results in the gasifying or volatilization of the photo-sensitive material and leaves only the phosphor in the desired pattern, the phosphor being held in place by surface forces;

The screen so produced may be coated if desired with a. protective coating such as ethyl silicate, potassium silicate, sodium silicate, silicon or silicone.

What-is claimed is: V

l. The method of preparing a tri-color fluorescent screen including the steps of coating a screen surface with a first light hardenable and heat gasifiable film of a photo-sensitive organic colloid, exposing designated areas of said first film to light through a mask to harden said designated,areas,.removing unexposed areas of said first film .to leave depressions at locations corresponding to i said unexposed areas, filling said depressions with a first phosphor and adhering said first phosphor to said screen maskto harden said designated areas, removing unex-.. posediareas to leave depressions at locations correspondingto; said unexposed areas, filling said depressions with a second phosphor and adhering said second phosphor to said screen surface, removing the exposedfand light. hardened .areas of said second film, coating said screen.

surface witha third light hardenable and heat gasifiable of alphoto-sensitive organic colloid, exposing previouslyiune'xposed designated areas of said. third film to light through a mask to harden said designated areas,

.4 removing unexposed areas to leave depressions at locations corresponding to said unexposed areas, filling said depressions with a third phosphor and adhering said third phosphor to said screen surface, and baking said screen to gasify remaining portions of said. light hardened films leaving behind said first, second, and third phosphors on said screen surface.

2. The method of preparing a tri-color fluorescent screen including the steps of coating a screen surface with a first light hardenable film of photo-sensitive material, exposing designated areas of said first film to light through a mask, washing said film with a solvent to remove unexposed areas of said first film and to leave depressions at locations corresponding to said unexposed areas, filling said depressions with a first phosphor and adhering said first phosphor to said screen surface, removing the exposed and light hardened areas of said first film, coating said screen surface with a second light hardenable film of photo-sensitivematerial, exposing previously unexposed designated areas of said second film to light through a mask, washing said second film with a solvent to remove unexposed areas and to leave depressions at locations corresponding to said unexposed areas, filling said depressions with a secondphosphor and adhering said second phosphor to said screen surface, removing the exposedand light hardened areas of said second film, coatof photo-sensitive material, exposing previously unexposed designated areas of said third film to light through a mask, washing said'third film with a solvent to remove unexposed areas and to leave depressions at locations corresponding to said unexposed areas, filling said depressions with a. third phosphor and adhering said third phosphor to said screen surface, and baking said screen to gasify remaining portions of said light hardened films leaving behind said first, second, and third phosphors on said screen surface.

3. The method. of preparing a tri-color fluorescent screen including the steps of coating a screen surface with a first light hardenable film of photo-sensitive material, exposing designated areas of said first film to light through a mask, washing said fihn with a solvent to remove unexposed areas of said first film and to leave depressions at locations corresponding to said unexposed areas, filling said depressions with a first phosphor and adhering said first phosphor to said screen surface, removing the exposed and light hardened areas of said first film, coating said screen surface with a second light hardenable film of photo-sensitive material, indexing said.

mask and exposing previously unexposed designated areas of said second film to light through said mask, washing said second film with a solvent to remove unexposed areas and to leave depressions at locations corresponding to said unexposed areas, filling said depressions wtih a second phosphor and adhering said second phosphor to said screen surface, removing the exposed and light hardened areas of said second film, coating said screen surface with a third light hardenable film of photosensitive material, indexing said mask and exposing previously unexposed designated areas of said third film to light through said mask, washing said third film with a solvent to remove unexposed areas and to leave depressions at locations corresponding to said unexposed areas, filling said depressions with a third phosphor and adhering said third phosphor tosaid screen surface, and baking said.

areas of said film to a light source through a negative whichpe rmits light to strike said film'in a predetermined pattern to harden said film in the exposed areas, washing the film-coated surface to remove the photo-resist from the unexposed areas of said film and to leave depressions of a predetermined design and pattern, filling said depressions with anadhesive, applying a first phosphor to said surface removing the remaining exposed areas of said film from said surface leavinggbehind a first phosphor pattern, recoating the entire surface with a light hardenable film of a photo-resist, exposing previ ously unexposed designated areas of said film to a light source through a negative which permits light to strike said film in a predetermined pattern to harden said film in the exposed areas, washing the film-coated surface to remove the photo-resist from the unexposed areas of said film and to leave depressions of a predetermined design and pattern, filling said depressions with an ad hesive, applying a second phosphor to said surface, removing the remaining exposed areas of said film to leave a second phosphor pattern and repeating the above steps of applying a light hardenable film of a photo-resist, exposing previously unexposed designated areas to light through a negative, washing to remove the unexposed film, filling the depression with adhesive, and applying a further phosphor until the desired multiple pattern screen ing a plurality of phosphors applied in a predetermined pattern, the steps comprising coating the surface on which the screen is to be formed with a light hardenable, water-V dispersible film of a photo-resist, exposing designated areas of said film to a light source through a negative which permits light to strike said film in a predetermined pattern to harden said film in the exposed areas, washing the film-coated surface with a stream of warm water to remove the photo-resist from the unexposed areas of said film and to leave depressions of a predetermined design and pattern, filling said depressions with an adhesive, applying a first phosphor to said surface, removing the remaining exposed areas of said film from said surface by immersion of said surface in a hot 3% hydrogen peroxide solvent solution leaving behind a first phosphor pattern, recoating the entire surface with a light hardenable, water-dispersible film of a photo-resist, exposing previously unexposed designated areas of said film to a light source through a negative which permits light to strike said filmin a predetermined pattern to harden said film in the exposed areas, washing the filmcoated surface to remove the photo-resist from the unexposed areas of said film and to leave depressions of a predetermined design and pattern, filling said depressions with an adhesive, applying a second phosphor to said surface, removing the remaining exposed areas of said film by immersing in said solvent solution to leave a second phosphor pattern and repeating the above steps of applying a film of a photo-resist, exposing previously unexposed designated areas to light through a negative, washing to remove the unexposed film, filling the depression with adhesive, and applying a further phosphor until the desired multiple pattern screen has been produced.

6. In the method of preparing a fluorescent screen having a plurality of phosphors in a predetermined pattern, the steps comprising coating the surface on which the screen is to be formed with a light hardenable film of a photo-resist, exposing designated areas of said film to a light source through a negative which permits light to strike said film in a predetermined pattern to harden said film in the exposed areas, washing the film-coated surface to remove the photo-resist from the unexposed areas of said film and to leave depressions of a predetermined design and pattern, filling said depressions with an adhesive, applying a first phosphor to said surface, removing the remaining exposed areas of said filmfrorn 6 said surfacein an enzyme solution leavingv behind a first phosphor pattern, recoating the entire surface with: a lighthardenable film of a photo-resist, exposing p'r'evi ousl y unexposed designated'areas of said film to a light:

source through a negative which permits light, to strike said 'filntlin a .pr'edeterrninedpattern to harden saidfilr'ri in"the exposed areas, washing the film-c oated surface, to remove'the photo-resist from the unexposed areas of's'aid film'and to leave depressions of a predetermineddesign and pattern, filling said depressions with an 'adhesive,'

applying a second phosphor to said surface, removing the remaining exposed areas of said film by immersing in said enzyme solution to leave a second phosphor pattern and repeating the above steps of applying a film of a photo-resist, exposing previously unexposed designated areas to light through a negative, washing to remove the unexposed film,"filling the depression with adhesive, and applying a further phosphor until the desired multiple pattern screen has been produced.

7. In the method of preparing a fluorescent screen having a plurality of phosphors applied in a predetermined pattern, the steps comprising coating the surface on which the screen is to be formed with a light hardenable film of a photo-resist, exposing designated areas of said film to a light source through a negative which permits light to strike said film in a predetermined pattern to harden said film in the exposed areas, washing the film-- coated surface to remove the photo-resist from the unexposed areas of said film and to leave depressions of a predetermined design and pattern, filling said depressions with an adhesive-phosphor mixture, removing the remaining exposed areas of said film from said surface leaving behind a first phosphor pattern, recoating the entire surface with a light hardenable film of a photoresist, exposing previously unexposed designated areas of said film to a light source through a negative which permits light to strike said film in a predetermined pattern to harden said film in the exposed areas, washing the film-coated surface to remove the photo-resist from the unexposed areas of said film and to leave depressions of a predetermined design and pattern, filling said depressions with an adhesive-phosphor mixture, removing the remaining exposed areas of said film to leave a second phosphor pattern and repeating the above steps of applying a light hardenable film of a photo-resist, exposing previously' unexposed designated areas to light through a negative, washing to removethe unexposed film, and filling the depression with adhesive-phosphor mixture until the desired multiple pattern screen has been produced. i

8. In the method of preparing a fluorescent screen having a plurality of phosphors applied in a predetermined pattern, the steps comprising coating the surface on which the screen is to be formed with a light hardenable film of a photo-resist, exposing designated areas of said film to a light source through a negative which permits light to strike said film in a predetermined pattern to harden said film in the exposed areas, washing the filmcoated surface to remove the photo-resist from the unexposed areas of said film and to leave depressions of a predetermined design and'pattern, filling said depressions with an ethyl silicate adhesive, applying a first 1 phosphor to said surface, removing the remaining exwith an ethyl silicate adhesive, applying a second pression with adhesive, ,dhdapplyihg a timber phosphor until the desired multiplepgttem screen has een pro;

" Referen ces Citedjir ,the file of this patent 4 I UNITED STATES PATENTS 

2. THE METHOD OF PREPARING A TRI-COLOR FLUORESCENT SCREEN INCLUDING THE STEPS OF COATING A SCREEN SURFACE WITH A FIRST LIGHT HARDENABLE FILM OF PHOTO-SENSITIVE MATERIAL, EXPOSING DESIGNATED AREAS OF SAID FIRST FILM TO LIGHT THROUGH A MASK, WASHING SAID FILM WITH A SOLVENT TO REMOVE UNEXPOSED AREAS OF SAID FIRST FILM AND TO LEAVE DEPRESSIONS AT LOCATIONS CORRESPONDING TO SAID UNEXPOSED AREAS, FILLING SAID DEPRESSIONS WITH A FIRST PHOSPHOR AND ADHERING SAID FIRST PHOSPHOR TO SAID SCREEN SURFACE, REMOVING THE EXPOSED AND LIGHT HARDENED AREAS OF SAID FIRST FILM, COATING SAID SCREEN SURFACE WITH A SECOND LIGHT HARDENABLE FILM OF PHOTO-SENSITIVE MATERIAL, EXPOSING PREVIOUSLY UNEXPOSED DESIGNATED AREAS OF SAID SECOND FILM TO LIGHT THROUGH A MASK, WASHING SAID SECOND FILM WITH A SOLVENT TO REMOVE UNEXPOSED AREAS AND TO LEAVE DEPRESSIONS AT LOCATIONS CORRESPONDING TO SAID UNEXPOSED AREAS, FILLING SAID DEPRESSIONS WITH A SECOND PHOSPHOR AND ADHERING SAID SECOND PHOSPHOR TO SAID SCREEN SURFACE, REMOVING THE EXPOSED AND LIGHT HARDENED AREAS OF SAID SECOND FILM, COATING SAID SCREEN SURFACE WITH A THIRD LIGHT HARDENABLE FILM OF PHOTO-SENSITIVE MATERIAL, EXPOSING PREVIOUSLY UNEXPOSED DESIGNATED AREAS OF SAID THIRD FILM TO LIGHT THROUGH A MASK, WASHING SAID THIRD FILM WITH A SOLVENT TO REMOVE UNEXPOSED AREAS AND TO LEAVE DEPRESSIONS AT LOCATIONS CORRESPONDING TO SAID UNEXPOSED AREAS, FILLING SAID DEPRESSIONS WITH A THIRD PHOSPHOR AND ADHERING SAID THIRD PHOSPHOR TO SAID SCREEN SURFACE, AND BAKING SAID SCREEN TO GASIFY REMAINING PORTIONS OF SAID LIGHT HARDENED FILMS LEAVING BEHIND SAID FIRST, SECOND, AND THIRD PHOSPHORS ON SAID SCREEN SURFACE. 